The possible role of fetal brain antigens in multiple sclerosis (MS) is being investigated. Extracts of human fetal brain will be prepared and antisera to these extracts will be produced in rabbits. With the use of a competitive binding radioimmunoassay the presence of fetal brain antigens in sera or CSF of MS patients and control groups will be investigated. Immune responses to fetal antigens in MS patients will be evaluated in two ways: a) The presence of a humoral immune response will be determined using an antibody mediated lymphocyte cytotoxicity assay in which isotopically labeled fetal brain cells are targets. b) The presence of a cellular immune response to fetal brain antigen will be determined utilizing a direct lymphocyte mediated cytotoxicity assay with isotopically labeled fetal brain cells as targets.